1. Field of the Invention
The present invention relates to an apparatus and a method for an image process. Particularly, the invention relates to a technique to embed additional information in image information.
2. Description of the Related Art
Recently, for content such as still images or moving images, it is demanded that copyright protection is provided, and security against copying is provided. In order to respond to this demand, techniques in which additional information is embedded in content data and the embedded information is read are advanced. As one of the techniques, there is an electronic watermark technique.
As a technique to embed additional information in a still image, there is a method of using a lower bit of pixel data. In this method, since the lower bit of the pixel data is changed and the additional information is embedded, the pixel data in which the additional information is embedded is grasped as a minute change in pixel value. In this method, in the case where the still image is hard copied, the change in the pixel value appears as degradation of image quality, and it is not preferable in the case where the hard copy is performed.
As a technique to embed additional information in an image which is to be hard copied, there is a following technique. The additional information is represented by a periodic component and is embedded in image data. In order to check the additional information after this image data is printed on a sheet, when the image is read, Fourier transform is used to analyze the additional information.
Besides, when additional information is added to image data, the addition is performed by gradation processing the output image data. However, when the gradation process is the gradation process using a frequency near the resolution of a print output apparatus, there is a problem that certain detection can not be performed when the additional information is detected. Thus, there is a case where the Nyquist frequency of the print output apparatus which is hard to visually recognize can not be used.
As a technique to embed additional information in image data and as a technique to use an error diffusion system, there is a technique disclosed in JP-A-2003-101761.